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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

WHITE METAL

263

group—which scarcely contain impurities of lead—the copper and lead are
at once determined simultaneously (see Electrolytic Determination of
Copper and Lead in Ordinary Brass). If, however, the lead is in the pre-
ponderance, it is separated and determined as sulphate, the copper being
then determined in the filtrate (see Determination of Lead and Copper in
Complex Brasses).

4.  DETERMINATION OF THE IRON AND ZINC.   The liquid from which the
lead and copper have been separated is used for the determination of the
iron and zinc as in ordinary brasses.

5.  DETERMINATION OF THE ARSENIC.   See Determination of Arsenic in
Tin.

B. Gravimetrically.—2 grams of the sample are acted on with
the least possible quantity of aqua regia at a gentle heat on a water-bath.
When the action is complete, the liquid is diluted with 10-15 c.c. of water
containing 2-3 grams of tartaric acid in solution, then rendered faintly
alkaline with sodium hydroxide solution and treated with colourless sodium
sulphide in very slight excess. The liquid is heated on a water-bath with
occasional shaking until the precipitate has settled and is then filtered by
decantation, hot water containing a little sodium sulphide being used for
washing. The filtrate, containing tin and antimony, is analysed according
to i and the precipitate, containing lead, copper, etc., according to 2.

i. DETERMINATION OF THE TIN AND ANTIMONY. The nitrate is made
up to i litre and 200 c.c. treated in a |-litre flask with 6 grams of potassium
hydroxide, 3 grams of tartaric acid and slowly and, if necessary, with cooling,
sufficient 30% hydrogen peroxide to decolorise the solution, that is, to
transform the sodium sulphide completely into sulphate. The liquid is
boiled for some time to expel excess of hydrogen peroxide, allowed to cool,
neutralised with saturated oxalic acid solution and treated with 5 grams
of solid oxalic acid, diluted to about 250 c.c. and subjected at the boiling
point to a moderate current of hydrogen sulphide for about an hour. The
solution is then allowed to cool somewhat in the stream of hydrogen sulphide
and the antimony sulphide filtered off and washed with i% oxalic acid
solution saturated with hydrogen sulphide.

Since this antimony sulphide may contain small quantities of tin, it is
dissolved in a mixture of 10-15 c.c. of cone, hydrochloric acid and 10-15
c.c. of 10% ammonium chloride solution, a few crystals of potassium chlorate
being added when the mixture begins to boil. After dilution with water,
the liquid is filtered, made slightly alkaline with ammonia, treated with
5 grams of oxalic acid, diluted to 150 c.c. and the boiling liquid again treated
with hydrogen sulphide. FILTER

(a) Determination of the tin. The two filtrates are united, rendered
distinctly alkaline with ammonia, acidified with acetic acid, and a current
of hydrogen sulphide passed through the solution for about three hours.
After a rest of about 30 minutes on a water-bath to facilitate the separation
of the precipitate, the latter is filtered off and washed with hydrogen sulphide
solution containing a little ammonium sulphate. The tin sulphide thus
obtained is dried at 120°, transformed by ignition into 'the oxide and the
latter weighed : Sn02 X 0-7881 == Sn. hydrogen sulphide precipitate)